Add mandarin support

[Slyne]

1. Add character error rate
2. Add get_aishell_data.py to download aishell data and process data
3. Add jasper_aishell.py to train model
4. Add jasper_aishell_infer.py to do inference
5. Add ASR_Jasper_Mandarin_Tutorial.ipynb as a tutorial for mandarin

[redoctopus]

Is the tutorial file necessary? It's highly similar to the existing ASR-Jasper-Tutorial.ipynb, which we are planning on removing since we are revamping the tutorials.
Maybe a more specific Mandarin ASR tutorial could be useful in the future, though I think that would be more focused on the differences between Mandarin and English ASR than a second version of the English tutorial.
@okuchaiev any thoughts?

[Slyne]

Is the tutorial file necessary? It's highly similar to the existing ASR-Jasper-Tutorial.ipynb, which we are planning on removing since we are revamping the tutorials.
Maybe a more specific Mandarin ASR tutorial could be useful in the future, though I think that would be more focused on the differences between Mandarin and English ASR than a second version of the English tutorial.
@okuchaiev any thoughts?

I also agree with that. Since mandarin asr is very similar to English version, maybe just jasper_aishell.py & jasper_aishell_infer.py are enough.

[Slyne]

Use eval_metric to replace use_wer param.

[redoctopus]

Thanks for the changes. Removing notebook and approving.